1. Technical Field
This invention relates generally to multilayer metal gaskets, and particularly to those having at least two active bead layers separated by a partial stopper layer.
2. Related Art
Multilayer metal gaskets are commonly used in engine applications to provide a seal between two members that are joined by bolting or other clamping means, such as between a cylinder head and an engine block, or between an exhaust manifold and the block.
Various gasket configurations are known to the art and serve a variety of purposes. A particular application to which the present invention is directed is one in which the gasket is required to be of minimal thickness and able to seal effectively under fairly low contact pressure or able to conform to protrusions or recessions at the seal interface, such as in a cylinder head application where the cylinder liner protrudes above the top sealing deck of the engine block. Under these less than ideal sealing conditions, it is difficult to construct a seal that satisfies all of the criteria that such an application calls for.
For example, U.S. Pat. No. 5,544,899 discloses a multilayer metal gasket having a pair of functional layers formed with aligned openings and aligned beads surrounding the openings. A partial stopper layer is interposed between the functional layers in surrounding relation to the openings. In some of the embodiments, the stopper layer extends only partially across the sealing beads, enabling the beads to collapse against themselves under a clamping load. The concern here is that the full collapse of the beads could cause at least some degree of overcompression and permanent deformation of the beads and thus impair the sealing performance of the gasket. In at least one other embodiment, the stopper layer spans the full width of the beads and is welded on the opposite sides as well as deformed into nesting relation with one of the two opposing beads. It will be appreciated that the stopper layer in this embodiment would serve to constrain the deformation of the gasket layer that it is joined to by being welded on opposite sides of the bead. Consequently, the constrained functional layer compresses at a much higher load than that of the other layer, and the overall compression strength of the gasket increases, making it perhaps unsuitable for those applications calling for minimal gasket thickness and low compressibility.
U.S. Pat. No. 5,628,518 discloses another type of multilayer metal gasket which requires the middle layer to be a full layer rather than only a partial layer. While this may be suitable for many gasket applications, the full middle layer adds to the over all thickness of the gasket and thus may not be suitable for applications calling for minimal gasket thickness.
It is an object of the present invention to overcome or greatly minimize the shortcomings of the known prior gaskets and to provide a gasket that is best suited to minimal thickness, low compression applications.